Gülce Alp

Comparison of Flexural Strength of Different CAD/CAM PMMA-Based Polymers: Comparison of Flexural Strength of Interim Resin Materials

PURPOSEnTo compare the flexural strength of different computer-aided design/computer-aided manufacturing (CAD/CAM) poly(methyl methacrylate)-based (PMMA) polymers and conventional interim resin materials after thermocycling.nnnMATERIALS AND METHODSnRectangular-shaped specimens (n = 15, for each material) (25 × 2 × 2 mm3 ) were fabricated from 3 CAD/CAM PMMA-based polymers (Telio CAD [T]; M-PM-Disc [M]; Polident-PMMA [P]), 1 bis-acrylate composite resin (Protemp 4 [PT]), and 1 conventional PMMA (ArtConcept Artegral Dentine [C]) according to ISO 10477:2004 Standards (Dentistry-Polymer-Based Crown and Bridge Materials). The specimens were subjected to 10,000 thermocycles (5 to 55°C). Three-point flexural strength of the specimens was tested in a universal testing machine at a 1.0 mm/min crosshead speed, and the flexural strength data (σ) were calculated (MPa). The flexural strength values were statistically analyzed using 1-way ANOVA, and Tukey HSD post-hoc test for multiple comparisons (α = 0.05).nnnRESULTSnFlexural strength values ranged between 66.1 ± 13.1 and 131.9 ± 19.8 MPa. There were significant differences among the flexural strengths of tested materials, except for between T and P CAD/CAM PMMA-based polymers (p > 0.05). CAD/CAM PMMA-based polymer M had the highest flexural strength and conventional PMMA had the lowest (p < 0.05). CAD/CAM PMMA-based T and P polymers had significantly higher flexural strength than the bis-acrylate composite resin (p < 0.05), and conventional PMMA (p < 0.0001), and significantly lower flexural strength compared to CAD/CAM PMMA-based M (p < 0.05).nnnCONCLUSIONSnThe flexural strength of CAD/CAM PMMA-based polymers was greater than the flexural strength of bis-acrylate composite resin, which had a greater flexural strength compared to conventional PMMA resin.

Fracture analysis of CAD-CAM high-density polymers used for interim implant-supported fixed, cantilevered prostheses

Statement of problem. The load‐to‐fracture performance of computer‐assisted design and computer‐assisted manufacturing (CAD‐CAM) high‐density polymer (HDP) materials in cantilevers is unknown. Purpose. The purposes of this in vitro study were to evaluate the load‐to‐fracture performance of CAD‐CAM–fabricated HDPs and to compare that with performance of autopolymerized and injection‐molded acrylic resins. Material and methods. Specimens from 8 different brands of CAD‐CAM HDPs, including Brylic Solid (BS); Brylic Gradient (BG); AnaxCAD Temp EZ (AE); AnaxCAD Temp Plus (AP); Zirkonzahn Temp Basic (Z); GDS Tempo‐CAD (GD); Polident (Po); Merz M‐PM‐Disc (MAT); an autopolymerized acrylic resin, Imident (Conv) and an injection‐molded acrylic resin, SR‐IvoBase High Impact (Inj) were evaluated for load‐to‐fracture analysis (n=5). CAD‐CAM specimens were milled from poly(methyl methacrylate) (PMMA) blocks measuring 7 mm in buccolingual width, 8 mm in occlusocervical thickness, and 30 mm in length. A wax pattern was prepared in the same dimensions used for CAD‐CAM specimens, flasked, and boiled out. Autopolymerizing acrylic resin was packed and polymerized in a pressure container for 30 minutes. An identical wax pattern was flasked and boiled out, and premeasured capsules were injected (SR‐IvoBase) and polymerized under hydraulic pressure for 35 minutes for the injection‐molded PMMA. Specimens were thermocycled 5000 times (5°C to 55°C) and fixed to a universal testing machine to receive static loads on the 10‐mm cantilever, vertically at a 1 mm/min crosshead speed until fracture occurred. Maximum load‐to‐fracture values were recorded. ANOVA was used to analyze the maximum force values. Significant differences among materials were analyzed by using the Ryan‐Einot‐Gabriel‐Welsch multiple range test (&agr;=.05). Results. Statistically significant differences were found among load‐to‐fracture values of different HDPs (P<.001). GD and Po materials had significantly higher load‐to‐fracture values than other materials (P<.001), and no statistically significant differences were found between GD and Po. The lowest load‐to‐fracture values were observed for autopolymerized and BG materials, which were significantly lower than those of GD, Po, AE, AP, Z, MAT, Inj, and BS. The load‐to‐fracture value of autopolymerized acrylic resin was not significantly different from that of BG CAD‐CAM polymer. Conclusions. GD and Po CAD‐CAM materials had the highest load‐to‐fracture values. AE, AP, Z, MAT, and BS CAD‐CAM polymers and injection‐molded acrylic resin had similar load‐to‐fracture values, which were higher than those of BG and autopolymerized acrylic resin. Autopolymerized acrylic resin load‐to‐fracture value was similar to that of BG CAD‐CAM polymer, which is colored in a gradient pattern.

Effect of surface treatments and coffee thermocycling on the color and translucency of CAD-CAM monolithic glass-ceramic

Statement of problem. The effects of surface treatments and coffee thermocycling on the color and relative translucency of a recently introduced computer‐aided design and computer‐aided manufacturing (CAD‐CAM) monolithic glass‐ceramic are unknown. Purpose. The purpose of this in vitro study was to evaluate the effect of coffee thermocycling on the color and relative translucency parameter (RTP) of CAD‐CAM monolithic glass‐ceramics after different surface treatments. Material and methods. Specimens (1.5‐mm‐thick) were sectioned from zirconia‐reinforced lithium silicate glass‐ceramic (ZLS) (n=18) and lithium disilicate glass‐ceramic (LDS) blocks (n=18). Two different types of surface treatments (glazing or polishing) were applied to the specimens. The specimens were subjected to 5000 thermocycles in a coffee solution. The color coordinates of specimens were measured before and after coffee thermocycling by using a spectroradiometer, and color differences and relative translucency values were calculated by using CIEDE2000 color difference and RTP formulas. ANOVA was used to analyze the color difference and relative translucency values by using maximum likelihood estimation and the Satterthwaite degrees of freedom methods. Any significant interaction between surface subgroups was further analyzed by using the Tukey‐Kramer adjustment (&agr;=.05). Results. Material type had a significant effect on color difference (P=.018). All color difference values of all materials were smaller than the clinical acceptability threshold (<1.8 units). For relative translucency, material (P<.001) and coffee thermocycling had a significant effect (P=.014), and an interaction was found between the surface treatments and materials (P<.001). The Tukey‐Kramer test revealed significant differences between glazed and polished subgroups of LDS material, except for ZLS‐glazed and ZLS‐polished subgroups. Conclusions. Different surface treatments of CAD‐CAM monolithic zirconia‐reinforced lithium silicate and lithium disilicate glass‐ceramics resulted in clinically acceptable color changes after coffee thermocycling. The color changes in all groups, except for LDS‐polished, were not perceivable. Lithium disilicate was more translucent than zirconia‐reinforced lithium silicate before and after coffee thermocycling. Coffee thermocycling decreased the translucency of both of the materials. Different surface treatments affected the translucency of only lithium disilicate for tested thickness.

Corrosion potential in artificial saliva and possible genotoxic and cytotoxic damage in buccal epithelial cells of patients who underwent Ni-Cr based porcelain-fused-to-metal fixed dental prostheses

Nickel-chromium(Ni-Cr) based alloys account for the majority of the porcelain-fused-to-metal fixed dental prostheses(PFM-FDPs) on account of their superior properties despite both nickel and chromium being known as human carcinogens. Understanding the genotoxicity and the cytotoxicity alongside the characteristics of corrosion behavior of the alloy is vital for understanding their biocompatibility. This study has evaluated whether the Ni-Cr based alloys corroded in artificial saliva by analyzing alloy decomposition at different pH levels and immersion durations(7, 14, 21, and 28u202fdays) using inductively coupled plasma-optic emission spectrophotometry(ICP-OES). The principal aim of the study was to determine the possible genotoxicity and cytotoxicity using micronucleus(MN) and other nuclear anomaly frequencies [nuclear bud(NBUD), binucleated(BNC), condensed chromatin(CC), karyorrhectic(KhC), pyknotic(PC) and karyolytic(KC) cells] and various cytome parameters [basal cells(BC), differentiated cells(DF)] with the buccal epithelial cell(BEC) micronucleus cytome assay(BMCyt). This test was administered at 1 pre- and 3 post-treatment time points to 40 patients who underwent installation of PFM-FDPs made of Ni-Cr based alloy. Furthermore, at the final post-treatment time point, saliva cotinine levels were measured with salivary cotinine quantitative enzyme immunoassay(EIA) kit and information obtained by questionnaire prior to the first pre-treatment time point was confirmed. The highest greatest release of Ni and Cr ions were seen at pH 2.3. MN and micronucleated cell frequencies, and BNC cell frequencies were significantly elevated at post-treatment time points(pu202f<u202f0.03). BC, CC, KhC, PC and KC cell frequencies however were not significantly different between pre-and post-treatment time points(pu202f>u202f0.05). MN frequency was significantly lower in non-smokers than in current and former smokers(pu202f<u202f0.001) at the pre-treatment time point. There was no significant correlation between the unit number of PFM-FDPs and MN frequencies. Our results revealed that Ni-Cr based alloys are prone to corrosion and that PFM-FDPs fabricated with Ni-Cr based alloys may induce genotoxic effects rather than cytotoxic effect.

In Vitro Evaluation of Adhesion of Candida albicans on CAD/CAM PMMA-Based Polymers: Adhesion of C. albicans on CAD/CAM PMMA-Based Polymers

PURPOSEnTo compare the amount of adherent Candida albicans to different CAD/CAM poly(methyl methacrylate) (PMMA)-based polymers and conventional heat-polymerized PMMA after long-term thermal cycling.nnnMATERIALS AND METHODSnThe specimens were subjected to 10,000 thermal cycles (5-55°C) and divided into two groups, uncoated and pellicle-coated. Surface roughness and contact angles of the specimens were measured. The surface morphology was observed with scanning electron microscopy (SEM). An adhesion test was performed by incubating the disk specimens in C. albicans suspensions at 37°C for 2 hours, and the adherent cells were counted under an optical microscope. The data were analyzed statistically using a variance analysis and Tukey HSD post hoc comparison test. The correlation between measurements was tested using a Pearson correlation analysis (α = 0.05).nnnRESULTSnCAD/CAM polymers generally showed statistically significant lowest Ra and contact angle values, whereas conventional PMMA showed the highest Ra and contact angle values in the uncoated group (p < 0.05). Pellicle coating essentially increased contact angle of all materials and reduced the differences in a number of Candida cells on the materials (p < 0.05). Candida adhesion was statistically significantly greatest on conventional PMMA when compared to CAD/CAM polymers. A strong positive correlation was found between the surface roughness of the specimens (p < 0.05) and the amount of adhered cells, whereas no correlation was found between hydrophobicity of the specimens and the amount of adhered cells (p > 0.05).nnnCONCLUSIONSnCAD/CAM PMMA-based polymers may be preferable to reduce Candida-associated denture stomatitis in long-term use.

Effect of different resin cements and surface treatments on the shear bond strength of ceramic-glass polymer materials

Statement of problem. The effect of different surface treatment techniques on the bond strength of different types of ceramic‐glass polymer computer‐assisted design and computer‐assisted manufacturing (CAD‐CAM) materials and resin cements after aging is unknown. Purpose. The purpose of this in vitro study was to evaluate the surface roughness of different ceramic‐glass polymer CAD‐CAM materials after 2 different surface treatments and the effect of material, surface treatment, resin cement, and aging on bond strength. Additionally, it was to determine any correlation between the surface roughness and bond strength. Material and methods. CAD‐CAM ceramic‐glass polymer materials, a polymer‐infiltrated ceramic network (PICN) (VITA ENAMIC), a resin nanoceramic (Lava Ultimate), and a nanoparticle‐filled resin (Cerasmart) (1.5 mm in thickness; n=144) were divided into 2 subgroups in terms of surface treatments: airborne‐particle abraded or silica‐coated. The surface roughness values of specimens were measured. Composite resin cylinders were prepared and bonded to the restorative specimens using 2 different types of resin cements (dual‐polymerizing [DP] and light‐polymerizing [LP]). Half of the specimens were stored in distilled water for 24 hours, while the other half were submitted to 5000 thermocycles. The shear bond strength was measured, and the failure modes of the specimens were evaluated. The data were analyzed with ANOVA and Tukey HSD tests (&agr;=.05). The correlation between roughness and bond strength values was analyzed using Pearson correlation analysis. Results. Material (P=.012) and surface treatment type (P=.031) significantly affected the surface roughness. For bond strength, significant interactions were found among the material type, surface treatment, resin cement, and aging factors (P=.009). No significant correlation was found between roughness and bond strength (P=.943). Conclusions. The surface treatment and resin cement type affected the bond strength and surface roughness of tested restorative materials. DP resin cement provided higher bond strength for airborne‐particle abraded nanohybrid composite resin materials. LP resin cement achieved a higher bond strength when used with silica‐coated, nanoparticle‐filled resin and PICN materials.

Effects of fabrication and shading technique on the color and translucency of new-generation translucent zirconia after coffee thermocycling

Statement of problem. The color stability and translucency of preshaded and externally shaded monolithic and veneered new generation translucent zirconia are not well known. Purpose. The purpose of this in vitro study was to investigate the effect of fabrication (veneered or monolithic) and shading (preshaded or externally shaded) techniques on the color and relative translucency of translucent zirconia after coffee thermocycling. Material and methods. Specimens of different thicknesses (0.5 mm for veneered and 1.5 mm for monolithic) were sectioned from preshaded and externally shaded translucent zirconia. Externally shaded specimens were colored by using the dipping technique. Externally shaded (Ext Mono) and preshaded (Pre Mono) monolithic zirconia specimens were sintered and glazed. Externally shaded (Ext Vene) and preshaded (Pre Vene) 0.5‐mm‐thick specimens were sintered, veneered with feldspathic porcelain (1 mm), and glazed. The color coordinates of specimens were measured with a spectroradiometer before and after 10 000 thermocycles in coffee solution. Color differences were calculated using CIEDE2000, and relative translucency parameter (RTP) values were calculated using the RTPCIEDE2000 formula. Analysis of variance (ANOVA) was used to analyze the CIEDE2000 color differences and RTP values (&agr;=.05). Results. Shading technique had a significant effect on the color difference values (P=.018). For the translucency data, the 3‐way ANOVA revealed a significant interaction between the fabrication technique and shading technique (P=.002). Each pair of material subgroups within each combination of fabrication technique and shading technique was found to have a significantly different RTP, except between Ext Vene and Pre Vene (P=.115). Conclusions. Externally shaded translucent zirconia had a greater color change in coffee than the preshaded translucent zirconia, either in monolithic or veneered form. Fabrication technique significantly affected the RTP, and the monolithic zirconia was more translucent than the veneered zirconia.

Optical properties and surface roughness of prepolymerized poly(methyl methacrylate) denture base materials

Statement of problem. Studies of the color stability, relative translucency, and surface roughness of newly introduced computer‐assisted design and computer‐assisted manufacturing (CAD‐CAM) prepolymerized poly(methyl methacrylate) (PMMA) denture base materials are lacking. Purpose. The purpose of this in vitro study was to evaluate the color stability, relative translucency, and surface roughness of conventional and different prepolymerized CAD‐CAM PMMA denture base materials after coffee thermocycling (CTC). Material and methods. Six disk‐shaped specimens (10×2 mm) were prepared from 3 different brands of prepolymerized CAD‐CAM PMMA and a conventional heat‐polymerized PMMA denture base material (N=24). Specimens were polished conventionally in 2 stages. The specimens were subjected to 5000 coffee thermocycles. The surface roughness (Ra) of each specimen was measured 3 times before and after CTC, using a contact profilometer, and the mean roughness (Ra) values were calculated. The color coordinates of the specimens were determined by using a noncontact spectroradiometer, and color differences and relative translucency parameter (RTP) values were calculated by using CIEDE2000 color difference and RTPCIEDE2000 formulas. ANOVA was used to analyze surface roughness values, CIEDE2000 color differences, and RTP values (&agr;=.05). Results. CTC did not change the color of the tested materials. However, with regard to relative translucency, 2‐way ANOVA revealed a significant interaction between the material and CTC (P=.011). Also, although CTC increased the surface roughness of all tested materials (P=.031), Ra values were lower than the plaque accumulation threshold of Ra=0.2 &mgr;m. Conclusions. Mean color changes in all materials were clinically imperceptible after 5000 coffee thermocycles. One tested material had significantly lower relative translucency than other materials before and after CTC. The surface roughness values of all tested denture base materials were below the plaque accumulation threshold.

Effect of shading technique and thickness on color stability and translucency of new generation translucent zirconia

OBJECTIVEnTo evaluate the effect of shading technique and thickness on the color stability and translucency of translucent zirconia after coffee thermocycling.nnnMETHODSnSpecimens in different thicknesses (1; 1.5; 2u202fmm) (nu202f=u202f4 for each thickness) were sectioned from translucent preshaded zirconia (Pre) and externally shaded zirconia (Ext). After sintering, specimens were glazed and subjected to 10,000 thermocycling in coffee solution. The color coordinates of specimens were measured with a spectroradiometer before and after coffee thermocyling. Color differences and relative translucency parameter (RTP) values were calculated with CIEDE2000 color difference and TPCIEDE2000 formulas. ANOVA was used to analyze the CIEDE2000 color difference and RTP values (αu202f=u202f0.05).nnnRESULTSnAccording to 2-way ANOVA, no significant effect of shading technique and thickness on the color difference values was found (Pu202f>u202f.05). According to 3-way ANOVA, a significant interaction between the shading technique and thickness (Pu202f<u202f.0001) was found for RTP. The RTP parameter decreased with the increase in the thickness. Ext specimens presented significantly higher RTP than Pre specimens (Pu202f<u202f.0001), except for between Ext 1u202fmm and Pre 1u202fmm (Pu202f=u202f.179).nnnCONCLUSIONSnNeither shading technique nor tested thicknesses affected the color of translucent zirconia. Shading technique and thickness affected the RTP of translucent zirconia. The RTP was inversely affected with the thickness of the material. Externally shaded zirconia presented higher RTP than preshaded zirconia for specimens thicker than 1u202fmm.nnnCLINICAL SIGNIFICANCEnDiscoloration with coffee was insignificant for the tested translucent zirconia in tested thicknesses (1, 1.5, 2u202fmm). When a translucent restoration is intended, thinner externally shaded translucent zirconia restorations should be preferred instead of preshaded translucent zirconia.

Effect of thickness on optical properties of monolithic CAD-CAM ceramics

OBJECTIVEnTo compare the effect of material and thickness on the color stability and relative translucency parameters (RTP) for monolithic ceramics subjected to coffee thermocycling.nnnMETHODSnFour specimens each at thicknesses of 0.5, 0,7 and 1u202fmm were sectioned from monolithic ceramics [preshaded monolithic zirconia (MonZr), lithium disilicate (LDS) and zirconia reinforced lithium silicate (ZLS)]. The specimens were glazed and subjected to 5000 coffee thermocycling. The color coordinates of specimens were determined with a spectroradiometer and color differences and RTP values were calculated with CIEDE2000 color difference and TPCIEDE2000 formulas. ANOVA was used to analyze CIEDE2000 color difference and RTP values (αu202f=u202f.05).nnnRESULTSnFor the color difference data, the 2-way ANOVA revealed a significant interaction between material and different thickness (Pu202f=u202f.002). Except for 0.5u202fmm thick ZLS material, all materials in all thicknesses studied presented color changes within the clinically acceptable limits after coffee thermocycling. For the RTP data, the 3-way ANOVA revealed a highly significant interaction between material and different thicknesses (Pu202f<u202f.001).nnnCONCLUSIONSnMaterial type and thickness can be expected to affect color change and relative translucency of the restorations made with preshaded MonZr, LDS and ZLS materials. Except for 0.5u202fmm thick ZLS material, color changes of all studied materials were within the clinically acceptable limits. Except ZLS material, color changes of other materials were not significantly affected by thickness. Staining in coffee was not found to affect translucency, and the materials translucency parameters were ranked from high to low as LDS, ZLS and MonZr at each thickness studied.